The invention relates to a tool for the cutting machining of a workpiece and to control over positioning of the cutting machining elements and to a method for the cutting machining including controlling that positioning.
Known tools of the type referred to herein serve for generating a nonplanar surface on a workpiece, in particular on a valve seat in the region of a cylinder head of an internal combustion engine. The nonplanar surfaces are distinguished in that, as seen in cross section, they comprise at least two segments of a broken line inclined relative to one another or a continuously curved line. In order to machine the surface, either the tool is set in rotation and brought into engagement with the workpiece to be machined or the workpiece is rotated and moved relative to the stationary tool. It is essential to have relative movement between the tool and the workpiece which enables at least one cutter plate of the tool to remove chips from the workpiece.
During machining of the nonplanar surface, the cutter plate is moved in the radial direction relative to an imaginary center axis of the tool or workpiece. Advancing movement of the tool or workpiece along the direction of this center axis occurs simultaneously.
The tool is distinguished in that it comprises a part-tool which is movable relative to the main body of the tool and which, for example, can execute a translational movement relative to the center axis. For example, the part-tool may be designed as a reamer which carries out fine machining on the inner face of a predrilled bearing bush for guiding a valve stem.
In known tools, the cutter plate is received by a holder, which cooperates with a coupling element designed as a slide in order to carry out the axial and radial movement of the cutter plate. An actuating device displaces the slide within the main body of the tool during the machining of the nonplanar surface of the workpiece. To avoid imbalance of the tool which occur as a result, a so-called counterslide is provided, which is intended to compensate the mass displacement within the main body. However, balancing of a tool of this type presents problems. Moreover, such a tool has a highly complicated design and is therefore of high cost.
In order to achieve this object, a tool is proposed for cutting machining a workpiece, including a cutter plate supported on a holder for machining a surface and additionally comprising a part-tool projecting from the body of the tool. The cutter plate is supported on a holder which is in turn supported on a rotatable eccentric such that rotation of the eccentric moves the holder radially. A cooperating converting device converts axial movement of an actuating device into rotation of the eccentric through intermeshing gear elements. The part-tool, e.g., a reamer, is moved by a second push/pull rod axially with respect to the body of the tool and into the workpiece, and the part-tool is supported on the axis of the main body.
The tool includes a coupling device which comprises an eccentric which is rotatable by the actuating device about an axis offset relative to the center axis of the tool. The holder of the cutter plate of the tool is mounted on the eccentric so that, when the eccentric is rotated, on the one hand, the holder is moved along an imaginary arcuate path and, on the other hand, the holder changes its distance relative to the center axis of the tool executes radial movement. During machining of the nonplanar surface of the workpiece by the cutter plate, an axial movement along the direction of the center axis is undergone at least by the holder, or else by the complete tool relative to the stationary workpiece or by the workpiece relative to the tool. Overall, this moves the cutter plate including movement components in the axial and in the radial direction.
In a preferred embodiment of the tool, the coupling device comprises a converting device which brings about the rotational movement of the eccentric and has at least two intermeshing threaded elements. The threaded elements are designed preferably as coarse-pitch threaded elements. One of the threaded elements is coupled to the actuating device and the other one is coupled to the eccentric. When the actuating device is activated, axial movement of the first threaded element is converted into rotational movement of the other threaded element, which rotates the eccentric and sets a radial position of the cutter plate. This tool is distinguished by a simple design which is not susceptible to faults and which can be implemented costeffectively.
In a preferred embodiment of the tool, one of threaded elements, and particularly the one coupled to the actuating device, comprises a sleeve with a thread on its inside. An embodiment of this kind is possible for use in a very small space, enabling very small tools to be produced.
In a further preferred embodiment of the tool, the actuating device is designed as a first push/pull rod. Actuating devices of this type are known and can therefore be coupled to existing machine tools in a simple way.
In a preferred embodiment of the tool, the part-tool comprises a reamer having a center axis which coincides with the center axis of the tool. This tool makes; it possible, for example, to generate the bearing surface for a valve, that is the valve seat, and to machine the bearing sleeve which guides the stem of a valve.
A method for the cutting and machining of a workpiece for generating a nonplanar surface is known. The nonplanar surface may, in particular, be a valve seat. To that extent, reference is made to the statements regarding the known tool. As stated above, during the machining of the nonplanar surface, the tool can rotate relative to a stationary workpiece, or vice versa. Here, too, it is essential only to have the relative movement between the tool and the workpiece, so that a cutter plate can remove chips from the surface to be machined.
It is known to move the tool up to the workpiece to be machined and to first machine the nonplanar surface, for example, the valve seat in the cylinder head of an internal-combustion engine. Thereafter, the part-tool, in this example a reamer, is moved out of the tool and introduced into the workpiece to be machined. In this case, the surface of the bearing bush for the valve stem is machined.
It has become apparent that during such machining, exact alignment between the valve seat and the valve stem bore cannot be assured. The surface quality and dimensional accuracy of the valve seat surface are often also not the best possible.
An object of the invention, therefore, is to provide a method which is distinguished in that the disadvantages mentioned here are avoided.
In order to achieve this object, a method is proposed which uses the tool of one of the two embodiments. The method is distinguished in that the tool is first moved up to the workpiece while the part-tool is drawn back into the main body of the tool. The part-tool is then introduced into the workpiece to be machined, in order, for example, to machine the bearing bush for the valve stem. This machining step exactly centers the tool relative to the workpiece. It is possible then, for example, to subsequently machine a second workpiece region using the at least one cutter plate of the tool in order to generate the nonplanar surface, with the cutter plate executing movement in the axial and the radial direction.
In a preferred embodiment of the method, at least at the commencement of the machining of the second workpiece region, the part-tool is introduced into the workpiece. The part-tool consequently centers the tool in the workpiece to be machined. When machining of the second workpiece region is begun, the tool or its at least one cutter plate is in an exactly defined position relative to the workpiece. This produces optimum alignment of the two surface regions of the workpiece which are machined with the aid of the tool.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.